Interpretation of Transistor Datasheets

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Hello All,

This along the lines of my previous 'High Side MOSFET' switch post
yesterday but in relation to transistors.

In some situations I'd like to use a PNP as a high side switch. I see
that some PNPs are -V & -I, and some are +V & +I. Visually, with the
base to the left, emitter up, and collector down... what is considered
+I vs. -I? I would assume E--->C is considered positive flow?

Also, that leads to datasheet data such as Vceo (collector emitter
voltage) of 40V. I assume the max V present at the collector is Ve +
40V? Or... Vceo of -40 is emitter can be Vc + 40?

Thanks,

John

 

[Rich Grise]

[crossposted to: sci.electronics.design,sci.electronics.basics
followups-to: sci.electronics.basics]

Hello All,

This along the lines of my previous 'High Side MOSFET' switch post
yesterday but in relation to transistors.

In some situations I'd like to use a PNP as a high side switch. I see that
some PNPs are -V & -I, and some are +V & +I. Visually, with the base to
the left, emitter up, and collector down... what is considered +I vs. -I?
I would assume E--->C is considered positive flow?

Also, that leads to datasheet data such as Vceo (collector emitter
voltage) of 40V. I assume the max V present at the collector is Ve + 40V?
Or... Vceo of -40 is emitter can be Vc + 40?

I've moved this thread over to .basics, because this is a basic question.

For one thing, it depends on if you're using conventional current flow
or electron flow. Generally, college guys use conventional, and techs
use electrons.

Anyway, the easy way to remember how current flows in a semiconductor
is that conventional current (which flows from positive to negative)
always flows in the direction the arrowhead is pointing. (well, except
in a Zener, and other unusual cases.)

As far as which they use on the data sheet, it's pretty much up to the
data sheet designer, although strictly speaking, all of the parameters
that are positive for an NPN become negative for a PNP, and vise versa.

Hope This Helps!
Rich

 

[Eeyore]

Hello All,

This along the lines of my previous 'High Side MOSFET' switch post
yesterday but in relation to transistors.

In some situations I'd like to use a PNP as a high side switch. I see
that some PNPs are -V & -I, and some are +V & +I. Visually, with the
base to the left, emitter up, and collector down... what is considered
+I vs. -I? I would assume E--->C is considered positive flow?

Also, that leads to datasheet data such as Vceo (collector emitter
voltage) of 40V. I assume the max V present at the collector is Ve +
40V? Or... Vceo of -40 is emitter can be Vc + 40?

I think you know which way round to collect a pnp transistor. Some manufacturers
state the polarity of the voltage, some don't bother. I guess they assume you
know it'll be negative.

Graham